The present invention relates to a control system for controlling a vehicle mounted hitch to which an implement can integrally attached.
Conventional hydro-mechanical hitch control systems typically include a large non-spring centered hitch command lever with a long operation range capable of moving stiff hydro-mechanical mechanisms. The operator could manipulate such a lever and set a depth and/or draft force operating point wherein the position of the lever would represent the set point. In a pure depth control mode, the lever position may represent the actual position of the hitch. In a draft force or a mixed draft force/depth control mode, the lever position will not normally represent the actual position of the hitch. In such a system there is no clear indication of whether or not the lever position is or is not indicative of the hitch position. This ambiguity often leads to operator confusion.
With the advent of electro-hydraulic hitch control systems, the need to move such stiff mechanisms has diminished, but electronic hitch control systems have continued to use such conventional hitch command levers. Examples of such hitch control systems are described in U.S. Pat. Nos. 6,216,072, 4,979,092, 4,518,044 and 4,508,176, all assigned to the assignee of the present application. Hitch systems with such command levers have been available on production tractors, including, for example, John Deere Model 8000 tractors.
In an electro-hydraulic hitch control system with such a conventional primary command lever, the operator may have incomplete command of the hitch, and incomplete feedback on how the control system is functioning. For instance, an operator may use one of the operator controls to command the hitch to move to a lower position. The hitch, however, may not lower for any number of reasons, with no indication of why it did not. The manipulated control may be, for the given conditions, an inappropriate choice. There may be mechanical reasons why the hitch did not lower, such as gauge wheels on an implement or very cold oil in the system. There may be operational reasons, such as other controls or inputs to the system, which prevent the hitch from responding as the operator intended.
In such a conventional hitch control system, the hitch control unit generates a setpoint parameter as a function of draft force or position, or a mixture of draft force and position, and controls the hitch in a closed-loop manner in response to the setpoint. In some circumstances, in a hitch control system with such a primary control lever, the lever must be temporarily disregarded (locked out) by the hitch control software until another event causes the lever to again become relevant. For example, if the hitch is moved due to actuation of another control (such as a raise-lower switch), then the control lever position no longer corresponds to the setpoint, and the control system must ignore the position of the control lever until the lever is moved to a position which again correlates to the setpoint.
Such a hitch control system may not produce predictable, repeatable results in response to small adjustments in hitch command during tractor operation. Such a hitch control system can cause operator frustration and can make proper setup and use of the hitch a difficult task.
One known commercially available hitch control system included a non-spring centered primary command or setting lever which was used to adjust the hitch operating setpoint, together with a separate spring-centered hitch switch or lever which could be used to raise or lower the hitch in an open-loop mode and which would override the command position set by the setting lever. Thus, it is believed that the primary hitch command lever was subject to the aforementioned problems.
An active depth control system has been available for towed implements such as field cultivator or chisel plow, wherein a hydraulic cylinder on the towed implement is controlled by a manually operated spring-centered control lever in the tractor cab. This known depth control system includes a “flick mode” wherein the towed implement is raised or lowered by a pre-set amount (such as a tenth of an inch) when the control lever is moved forward or back slightly and released. But, such a control mode has not been possible with the conventional control systems for integral type hitches.
It would be desirable to have a control system for an integral type hitch with a primary control lever which is never is locked out, so that the operator can always use that primary control lever for command of hitch movement.